1. Field of the Invention
This invention relates generally to a battery cell with integrated external wiring and, more particularly, to a battery cell for an electric vehicle battery pack which includes printed-on or surface-applied wires on the exterior of the cell, where the wires connect the positive and negative terminals of the cell to a location convenient for the attachment of a cell monitoring controller, and the wires can be resistive to facilitate cell discharging for the purpose of state of charge equalization.
2. Discussion of the Related Art
Electric vehicles and gasoline/electric hybrid vehicles are rapidly gaining popularity in today's automotive marketplace. Electric and hybrid vehicles offer several desirable features, such as reduced emissions, reduced usage of petroleum-based fuels, and potentially lower operating costs. A key component of both electric and hybrid vehicles is the battery pack. Battery packs in these vehicles typically consist of numerous interconnected cells, which can deliver a lot of power on demand. In order to maximize vehicle driving range and maximize battery pack life, the cells in the battery pack must be controlled during charging and discharging so that all cells are maintained at a fairly uniform charge level, and within a prescribed temperature range.
In many battery packs, each cell is connected to a cell monitoring controller, which monitors voltage and temperature conditions in each cell, and controls charging and discharging current. The positive and negative terminals of each battery cell are typically connected to a cell monitoring controller via jumper wires. Connecting the jumper wires to both the cell terminals and the cell monitoring controller requires extra steps in the assembly of the battery pack, and the jumper wires represent extra parts which must be handled during battery pack assembly. In addition, it is often impractical to attach the cell monitoring controller jumper wires after battery pack assembly, as the terminals are physically inaccessible at that point.
Individual battery cells must sometimes be discharged slightly in order to equalize the state of charge between cells. This discharging is currently also handled by the cell monitoring controllers. However, dissipating power through a resistor in the cell monitoring controller is not an ideal situation, as the resultant heat causes the temperature of the circuit board in the cell monitoring controller to increase. Adding a heat dissipation feature to the cell monitoring controller further raises the cost of that device.
It would be advantageous to apply wiring directly to the outside surface of the battery cell, via a wire printing technique or otherwise. Such surface-applied wiring could be directly connected to the terminals of the cell and could be routed to a location convenient for connection to the cell monitoring controller. Using resistive wiring for this purpose would also allow the surface-applied wires to serve as power-dissipating resistors for state of charge equalization, and the resultant heat to be absorbed in the battery cell, enabling simplification and cost reduction of the cell monitoring controller.